1. Field of the Invention
This invention relates to rotodynamic pumps, and specifically relates to means for controlling and automating the adjustment devices for restricting fluid recirculation and reducing wear between rotating and non-rotating fluid processing elements of rotodynamic pumps, especially those pumps that are suitable for handling slurries and those pumps that are, or can be, configured with adjustable wear components designed as leakage restricting devices.
2. Description of Related Art
Rotodynamic pumps, such as centrifugal pumps, are commonly known and used for pumping fluids in many types of industries and for many applications. Such pumps generally comprise an impeller (rotating element) housed within a pump casing (non-rotating element) having a fluid inlet and fluid outlet, or discharge. The impeller is typically driven by a motor external to the casing. The impeller is positioned within the casing so that fluid entering the inlet of the casing is delivered to the center, or eye, of the impeller. Rotation of the impeller acts on the fluid primarily by the dynamic action of the impeller vanes which, combined with centrifugal force, move the fluid to the peripheral regions of the casing for discharge from the outlet.
The dynamic action of the vanes, combined with centrifugal forces resulting from impeller rotation, produces pressure gradients within the pump. An area of lower pressure is created nearer the eye of the impeller and an area of higher pressure results at the outer diameter of the impeller and in the volute portion of the casing. An area of pressure change, from higher to lower pressure exists in the radially extending gap located between the rotating and non-rotating components. The pressure differential within the pump leads to fluid recirculation through the radial gap, between areas of high and low pressure. Such fluid recirculation, typically characterized as leakage, results in a consequential loss of pump performance and a dramatic increase in wear when there is a presence of solid particles in the fluid.
Therefore, pumps are structured with various leakage restricting devices, both on the drive side of the impeller to prevent or restrict external leakage, and on the inlet or suction side of the impeller to prevent or restrict internal recirculating leakage. Pump leakage-restricting or sealing mechanisms have been developed where a side liner, or wear plate, is placed in axial juxtaposition to the impeller of the pump. The side liners, usually corresponding to a suction side and a drive side of the pump, are positioned to abut the pump casing and, in some configurations, may be bolted to the pump casing. In other configurations, the side liners are mounted near the pump casing so that the axial position of the side liners relative to the impeller is adjustable.
The side liners may be metal, ceramic or elastomer material, or a combination of materials, and provide a simplified construction for repair or maintenance of the pump. Constructing the side liners with an elastomer seal to allow adjustability of a complete suction side or drive side has proven beneficial to extend the wear life of the liners. Additionally, a side liner provides a beneficial extension of the service life of the suction side seal face in heavy duty slurry applications versus adjusting only a seal wear ring. (Hill U.S. Pat. No. 5,941,536).
Radially-extending gaps, or tapered gaps that are substantially radially-extending, between the rotating and non-rotating members are much less prone to entrapment of solids and are commonly employed in slurry pumps. Nevertheless, leakage restricting arrangements are widely used in the radial gap between the rotating and non-rotating elements, whether on the drive side or suction side, to further restrict leakage and solids entrapment. For example, US Published Application No. 2004/0136825 to Addie, et al. discloses a fixed projection on either the pump casing or on the impeller to provide a leakage restricting arrangement between the impeller and the pump casing. These restriction configurations may suffer from declining performance in service if an adjustment means is not present to compensate for wear. Seal rings, or wear rings, which generally extend between the rotating and non-rotating elements are also used as leakage restricting devices.
Methods of adjusting seal rings and side liners are known and employed in rotodynamic pumps. For example, U.S. Pat. No. 4,527,948 to Addie, et al., describes a means of manually adjusting a seal to contact the impeller. U.S. Pat. No. 5,971,704 to Blattmann is similar to the '948 patent in that it discloses the use of threaded pusher bolts to manually adjust a small seal ring toward the impeller to a set clearance. These sealing arrangements force a wear ring towards the surface of the impeller. Such adjustment systems rely on manual adjustments of the mechanism. Following the manual adjustment of the seal, a period of time exists where there is a forcible contact between the rotating and non-rotating elements, but as the elements wear, a clearance between the two components develops. Uncontrolled or unmonitored clearances between the components allow leakage, which accelerates wear. Additionally, the clearance between the rotating and non-rotating elements will become progressively larger until a further adjustment is made.
U.S. Pat. No. 6,739,829 to Addie discloses an adjustable, floating ring element positioned between the impeller and the pump casing, which is also configured with means for receiving and distributing cooling and flushing fluid into the gap between the impeller and pump casing. The leakage restricting ring relies on water to flush the leakage restricting mechanism and provide the force to maintain its proximity to the impeller. The required flush system must be able to provide a consistent supply of clean liquid to the seal mechanism at a pressure which is not high enough to cause damage to the seal, but is sufficiently high enough to overcome internal pressures in the pump. The sufficiency of the pressure required in the flush system is dependent upon the application and the pump.
U.S. Pat. No. 6,599,086 to Soja describes an adjustable wear plate for a rotodynamic pump. The disclosed wear plate also uses a manual adjustment mechanism to position a complete side liner.
Prior adjustment mechanisms for sealing arrangements and side liners have heretofore been specifically directed to providing a manual means of adjustment. As a result, such arrangements may still be vulnerable to over adjustment and/or lack of sufficient adjustment, which may lead to undesirable fluid recirculation, or leakage, and wear between rotating and stationary elements of the pump. Moreover, flush water is not always available or practical for a given application. Further, the relative position of the sealing elements or leakage restricting mechanisms may not be accurately controlled by manual adjustment means due to variables of the application.
Thus, it would be advantageous in the art to provide a means for effecting automatic adjustment of the leakage restricting mechanism associated with the radial gap between rotating and non-rotating elements of the pump to control leakage and wear, thereby improving the life of the elements and performance of the pump. It would also be advantageous to provide a monitoring mechanism whereby the adjustment can be made automatically responsive to a detected need to effect an adjustment to the preferred gap between the rotating and non-rotating elements. It would also be advantageous to provide in a rotodynamic pump a sensor device that indicates one or more conditions within the pump so that manual adjustment can be effected.